Objects emit and/or reflect light. Systems and devices are oftentimes employed, for example in sensing systems, to detect the light emitted and/or reflected from objects. Such systems are used to discern the nature of the object.
Light emitted and/or reflected from objects can exhibit differing wavelengths. For example, objects emit and/or reflect light in the visible waveband (0.4-0.7 microns), which is that waveband discernible by the human eye. In addition, however, objects emit and/or reflect light in other wavebands, for example in the infrared (IR) waveband (1-20 microns). There are various systems for detecting light in differing wavebands.
For example, a focal plane array (FPA) is a device comprised of a plurality of light-sensing pixels. The light-sensing pixels are typically comprised of a material that is sensitive in a particular waveband based upon how the system is to be used, e.g., whether it is desired for detection of visible light or infrared light.
Oftentimes, there is a front-end optical train that focuses the light emitted and/or reflected from an object onto the FPA. In addition, there is typically a computing device communicatively coupled to the FPA for receiving electrical signals from the FPA. Upon receipt, the computing device can store data indicative of the electrical signals and/or analyze the data as needed for a particular application.
Light emitted and/or reflected from objects can also be filtered. The filtering of the light can lead to additional information about a scene or an object in a scene. For example, polarization content in light waves can be used to analyze a scene or an object.
In this regard, light waves are electromagnetic waves made up of both electric and magnetic fields. As light waves propagate, the electric and magnetic fields vibrate in a geometric plane that is oriented orthogonally to the direction of travel of the light. Polarization is a property of electromagnetic waves that describes the orientation of the electromagnetic waves in such an orthogonal plane.
An imaging polarimeter refers to a device that measures the orientation of the various electric field components contained in light emitted from and/or reflected from an object or a scene. Notably, the degree to which light that is emitted and/or reflected by an object or a scene is “polarized” is a complex function of the material makeup, surface roughness, and look angle between the observer and the surface normal of an object facet because of the geometry, roughness and material properties of the objects embedded in the scene.
Measurement of the polarization content of a scene improves the ability to detect and discriminate objects over that provided by conventional intensity imaging. This is in part because man-made objects tend to exhibit a higher degree of polarization than natural background. Polarimetric imaging exploits this property to provide increased detectability and discrimination over conventional intensity imaging.